[jira] [Commented] (OAK-4681) Automatically convert *all* "or" queries to "union" for SQL-2

["Thomas Mueller (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/OAK-4681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15594521#comment-15594521 ] 

Thomas Mueller commented on OAK-4681:
-------------------------------------

Yes, using "union" in some cases can reduce performance. However, the way this is done (for SQL-2, OAK-1617) is:

* first get the cost of the original query (with "or" condition)
* then get the cost of the union query
* pick the one that has a lower cost

So, if Lucene reports a lower cost with "or", then the query is not converted to union.

> Automatically convert *all* "or" queries to "union" for SQL-2
> -------------------------------------------------------------
>
>                 Key: OAK-4681
>                 URL: https://issues.apache.org/jira/browse/OAK-4681
>             Project: Jackrabbit Oak
>          Issue Type: New Feature
>          Components: query
>            Reporter: Thomas Mueller
>            Assignee: Thomas Mueller
>             Fix For: 1.6
>
>
> Currently, in OAK-1617, simple SQL-2 queries that contain "or" are converted to "union" if the cost is lower. However, more complex queries are not converted, see AndImpl.java, convertToUnion(), "in this case prefer to be conservative and don't optimize. This could happen when for example: WHERE (a OR b) AND (c OR d)." 
> It is implemented for XPath, and works fine there, so I think it is reasonable to do that for SQL-2 as well for trunk.



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